Active material for battery, nonaqueous electrolyte
battery, and battery pack

ABSTRACT

In general, according to one embodiment, the active material for a battery contains a niobium composite oxide represented by the formula: Li x M (1-y) Nb y Nb 2 O (7+δ) . M represents at least one kind selected from the group consisting of Ti and Zr. X, y, and δ are numbers respectively satisfying the following: 0≦x≦6, 0≦y≦1, and −1≦δ≦1). The pH of the active material for a battery is from 7.4 to 12.5.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority fromthe Japanese Patent Application No. 2013-062863, filed Mar. 25, 2013 andNo. 2014-040947, filed Mar. 3, 2013 which are incorporated herein byreference.

FIELD

Embodiments described herein relate generally to an active material fora battery, a nonaqueous electrolyte battery, and a battery pack.

BACKGROUND

Recently, a nonaqueous electrolyte battery such as a lithium-ionsecondary battery has been developed as a battery having a high energydensity. The nonaqueous electrolyte battery is expected to be used as apower source for hybrid vehicles or electric cars. Further, it isexpected to be used as an uninterruptible power supply for base stationsfor portable telephone, and the like. For this, the nonaqueouselectrolyte battery is desired to have other performances such as rapidcharge/discharge performances and long-term reliability. For example, anonaqueous electrolyte battery enabling rapid charge/discharge not onlyremarkably shortens the charging time but also makes it possible toimprove performances of the motive force of a hybrid vehicle and toefficiently recover the regenerative energy of them.

In order to enable rapid charge/discharge, it is necessary thatelectrons and lithium ions can migrate rapidly between the positiveelectrode and the negative electrode. When a battery using a carbonbased material in the negative electrode repeats rapid charge/discharge,dendrite precipitation of metal lithium is occurred on the electrode.Dendrite causes internal short circuits, which can lead heat generationand fires.

In light of this, a battery using a metal composite oxide as a negativeelectrode active material in place of a carbonaceous material has beendeveloped. Particularly, in a battery using a titanium oxide as thenegative electrode active material, rapid charge/discharge can beperformed stably. Such a battery also has a longer life than those usinga carbonaceous material.

However, the titanium oxide has a higher (nobler) potential than thecarbonaceous material relative to metal lithium. Further, the titaniumoxide has a lower capacity per weight. Thus, a battery formed by usingthe titanium oxide has a problem such that the energy density is low.

The potential of the electrode using the titanium oxide is about 1.5 Vbased on metal lithium and is higher (nobler) than that of the negativeelectrode using the carbonaceous material. The potential of the titaniumoxide is due to the redox reaction between Ti³⁺ and Ti⁴⁺ when lithium iselectrochemically inserted and released. Therefore, it is limitedelectrochemically. Further, there is the fact that rapidcharge/discharge of lithium ion can be stably performed at an electrodepotential as high as about 1.5 V. Therefore, it is substantiallydifficult to drop the potential of the electrode to improve energydensity.

As to the capacity of the battery per unit weight, the theoreticalcapacity of a lithium-titanium composite oxide such as Li₄Ti₅O₁₂ isabout 175 mAh/g. On the other hand, the theoretical capacity of ageneral graphite type electrode material is 372 mAh/g. Therefore, thecapacity density of the titanium oxide is significantly lower than thatof the carbon type material. This is due to a reduction in substantialcapacity because there are only a small number of lithium-adsorbingsites in the crystal structure and lithium tends to be stabilized in thestructure.

In view of such circumstances, a new electrode material containing Tiand Nb has been examined. Such a material is expected to have highcharge/discharge capacity. Particularly, the theoretical capacity of acomposite oxide represented by TiNb₂O₇ exceeds 300 mAh/g. However, thereis a problem such that, in such an oxide which reacts at a highpotential like about 1.5 V vs Li/Li⁺, any surface film is hard to beformed, and thus decomposition of an electrolyte solution on theelectrode surface (that is, a side reaction) is easily continued.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a pattern diagram showing a crystal structure of a niobiumcomposite oxide (TiNb₂O₇) in an active material for a battery of a firstembodiment;

FIG. 2 is a pattern diagram showing the crystal structure of FIG. 1 fromanother direction;

FIG. 3 is a cross-sectional view showing a flat type nonaqueouselectrolyte battery according to a second embodiment;

FIG. 4 is an enlarged sectional view of an A portion of FIG. 3;

FIG. 5 is an exploded perspective view showing a battery pack accordingto a third embodiment;

FIG. 6 is a block diagram showing the electric circuit of the batterypack of FIG. 5;

FIG. 7 is an X-ray diffraction pattern of the niobium composite oxide(TiNb₂O₇) in Example 1;

FIG. 8 is an infrared diffuse reflectance spectrum (1300 to 1600 cm⁻¹)of the niobium composite oxide (TiNb₂O₇) in Example 1 and Comparativeexample 1;

FIG. 9 is an infrared diffuse reflectance spectrum (2200 to 2500 cm⁻¹)of the niobium composite oxide (TiNb₂O₇) in Example 1 and Comparativeexample 1; and

FIG. 10 is an infrared diffuse reflectance spectrum after absorption ofpyridine in the niobium composite oxide (TiNb₂O₇) in Comparative example1.

DETAILED DESCRIPTION

In general, according to one embodiment, the active material for abattery contains a niobium composite oxide represented by the formula:Li_(x)M_((1-y))Nb_(y)Nb₂O_((7+δ)). M represents at least one kindselected from the group consisting of Ti and Zr. X, y, and δ are numbersrespectively satisfying the following: 0≦x≦6, 0≦y≦1, and −1≦δ≦1). The pHof the active material for a battery is from 7.4 to 12.5.

Hereinafter, the embodiments will be described with reference to theattached drawings.

First Embodiment

The active material for a battery according to the first embodimentcontains the niobium composite oxide represented by the formula:Li_(x)M_((1-y))Nb_(y)Nb₂O_((7+δ)) (wherein M represents at least onekind selected from the group consisting of Ti and Zr, x, y, and δ arenumbers respectively satisfying the following: 0≦x≦6, 0≦y≦1, and −1≦δ≦1)and the pH is from 7.4 to 12.5.

The crystal structure of the niobium composite oxide will be explainedwith reference to FIGS. 1 and 2.

As shown in FIG. 1, in the crystal structure of monoclinic niobiumcomposite oxide (TiNb₂O₇), metal ions 101 and oxide ions 102 formskeletal structures 103. Nb and Ti ions are randomly located in a metalion 101 at a Nb/Ti ratio of 2:1. The skeletal structures 103 arearranged three-dimensionally alternately, and a void 104 is formedbetween the skeletal structures 103. The void 104 serves as a host oflithium ion.

In FIG. 1, areas 105 and 106 are portions with two-dimensional channelsin directions [100] and [010]. As shown in FIG. 2, in each region, inthe crystal structure of monoclinic TiNb₂O₇, a void 107 is present in adirection [001]. The void 107 has a tunnel structure advantageous forthe conduction of lithium ions and serves as a conduction pathconnecting the areas 105 and 106 in a [001] direction. Therefore,lithium ions can go back-and-forth between the areas 105 and 106 throughthe conduction path.

Thus, the monoclinic crystal structure has an equivalently large spaceinto which lithium ions are inserted and has a structural stability.Further, the structure has two-dimensional channels enabling rapiddiffusion of lithium ions and conduction paths connecting these channelsin the direction [001]. Then, the lithium ions are inserted into andreleased from the insertion spaces effectively, and the insertion andrelease spaces for lithium ions are effectually increased. Therefore,the monoclinic crystal structure can provide a high capacity and highrate performance.

When lithium ions are inserted in the void 104, the metal ion 101constituting the skeleton is reduced to a trivalent one, therebymaintaining electroneutrality of a crystal. In the monoclinic oxiderepresented by TiNb₂O₇, not only a Ti ion is reduced from tetravalent totrivalent but also an Nb ion is reduced from pentavalent to trivalent.For this, the number of reduced valences per active material weight islarge. Therefore, the electroneutrality of the crystal can bemaintained, even if many lithium ions are inserted. For this, the energydensity of the oxide is high than that of a compound only containing atetravalent cation, such as the titanium oxide. The theoretical capacityof the monoclinic oxide represented by TiNb₂O₇ is about 387 mAh/g and ismore than twice the value of a titanium oxide having a spinel structure.

The monoclinic oxide represented by TiNb₂O₇ has about a lithiumadsorbing potential of 1.5 V (vs. Li/Li⁺). Therefore, a battery which isexcellent in rate performance, is capable of stably repeatingcharge/discharge, and has high energy density can be provided by usingthe active material having a crystal structure represented by TiNb₂O₇.

As an example of M, y, and δ in the formula M_((1-y))Nb_(y)Nb₂O_((7+δ)),M represents Ti, y represents 0, and δ represents 0. In this case, thecomposition formula of the niobium composite oxide is TiNb₂O₇. Asanother example, M represents Ti or Zr at a ratio of 0.9 to 0.1, yrepresents 0, and δ represents 0. In this case, the composition formulaof the niobium composite oxide is Ti_(0.9)Zr_(0.1)Nb₂O₇. Further, asanother example, M represents Ti, y represents 0.1 and δ represents0.05. In this case, the composition formula of the niobium compositeoxide is Ti_(0.9)Nb_(2.1)O_(7.05). As another example, M representseither Ti or Zr, y represents 1, and δ represents 0.5. In this case, thecomposition formula of the niobium composite oxide is Nb₃O_(15/2), thatis, Nb₂O₅.

The niobium composite oxide represented by the formulaLi_(x)M_((1-y))Nb_(y)Nb₂O_((7+δ)) preferably has the crystal structureof the monoclinic oxide. More preferably, it has a symmetry of spacegroup C2/m or P12/m1. It may be a crystal structure having atomiccoordination described in Non Patent Literature 2.

It has been found that the solid acid site concentration of the niobiumcomposite oxide represented by the formulaLi_(x)M_((1-y))Nb_(y)Nb₂O_((7+δ)) is high. The electrolyte solution usedfor the nonaqueous electrolyte battery is easily decomposed at the solidacid site of the active material for a battery. This becomes a factor ofa reduction in charge/discharge efficiency of the battery. As the resultof decomposition, decomposition products such as lithium fluoride andlithium oxide are accumulated on the surface of the active material, andthe resistance of the battery is increased. These matters cause a fallin performances of the battery, such as the lifespan performance and thehigh-current performance thereof.

When the pH of the active material for a battery of the first embodimentis set to a range of 7.4 to 12.5, the solid acid site concentration canbe greatly reduced, and the first cycle charge/discharge efficiency canbe dramatically improved. The pH value may be achieved by arrangingcarbonate ions on at least one part of the surface. Particularly,lithium carbonate is arranged on at least one part of the surface sothat the first cycle charge/discharge efficiency can be dramaticallyimproved, and excellent charge/discharge characteristics can berealized. The pH is preferably from 7.8 to 12.5, more preferably from9.0 to 11.0.

In the present application, the pH of the active material for a batterymeans a value measured by extraction at normal temperature (JISK5101-17-2:2004). Specifically, it is a pH value obtained by adding 1 gof the active material for a battery to 50 g of distilled water,vigorously shaking the resultant mixture for 1 minute, allowing it tostand for 5 minutes, and measuring the pH with a pH meter.

In this regard, the pH of the active material for a battery may varyaccording to the specific surface area. In other words, if the sizes ofthe same active materials for a battery when measured are different fromeach other, the specific surface areas change. As a result, they mayexhibit a different pH. The active material for a battery according tothe embodiment preferably shows the above pH as measured when thespecific surface area is from 0.5 to 50 m²/g. Further, the activematerial preferably shows the above pH as measured when the specificsurface area is from 3 to 30 m²/g. In this regard, when the specificsurface area is out of the range of 0.5 to 50 m²/g, or out of the rangeof 3 to 30 m²/g, the active material may show a pH out of the above pHrange.

The effect of the first embodiment can be obtained by arrangingcarbonate ions on one part of the surface. When the surface is coveredwith carbonate ions, a higher effect can be obtained. In the activematerial, the reactivity of the active material with the electrolytesolution is suppressed, and the first cycle charge/discharge efficiencyis increased. Further, this contributes to large current characteristicsand excellent charge/discharge cycle performance.

The niobium composite oxide represented by the formula:Li_(x)M_((1-y))Nb_(y)Nb₂O_((7+δ)) contained in the active material for abattery of the first embodiment is preferably granular.

The carbon content of the active material for a battery of the firstembodiment is preferably from 0.01 to 3% by mass based on the total massof the active material. More preferably, the carbon content of theactive material for a battery of the first embodiment is from 0.01 to 1%by mass based on the total mass of the active material. When carbonateions having a carbon concentration of 0.01% by mass or more arearranged, a sufficient effect can be obtained, a side reaction with anelectrolyte solution can be decreased, and excessive formation of highresistance films can be suppressed. Even if carbonate ions on thesurface become excessive, the effect of the first embodiment can beobtained. However, this leads to a decrease in capacity of the activematerial. In addition, the active material itself becomes a resistivecomponent. Accordingly, the carbon concentration is set to preferably 3%by mass or less, more preferably 1% by mass or less.

The carbon content in the niobium composite oxide represented by theformula: Li_(x)M_((1-y))Nb_(y)Nb₂O_((7+δ)) can be quantified by the highfrequency heating-infrared absorption method. For example, the titaniumcomposite oxide taken out from the battery is dried at 150° C. for 12hours, weighed and placed in a container, and measured with ameasurement device (e.g., CS-444LS, manufactured by LECO Corporation).

The state of carbon can be determined with an electron probe microanalyzer (EPMA) which is applied to the cross section of the activematerial, for example, by line analysis or carbon mapping.

Alternatively, when carbonate ions (CO₃ ⁻) are arranged on at least onepart of the surface of the niobium composite oxide represented by theformula Li_(x)M_((1-y))Nb_(y)Nb₂O_((7+δ)), the existence of carbonateions (CO₃ ⁻) can be confirmed with Fourier transform infraredspectrophotometer (FT-IR). A peak from the carbonate ion (CO₃ ⁻) appearsin the range of 1430±30, the range of 1500±30, or the range of 2350±30cm⁻¹ in an infrared reflectance spectrum.

The niobium composite oxide can be taken out from a battery by a methoddescribed hereinafter. The battery is dismantled in the state ofdischarge, and then one of its electrodes (for example, negativeelectrode) is taken out and washed with methylethyl carbonate. Thewashed negative electrode layer is inactivated in water. The niobiumcomposite oxide in the negative electrode layer is extracted with acentrifugal separator.

The active material for a battery according to the first embodiment canbe used not only for a negative electrode but also for a positiveelectrode, excellent charge/discharge cycle performance can be obtainedeven in either case. That is, the charge/discharge cycle performance isan effect obtained by arranging carbonate ions on the surface. Even ifthe active material is used for the negative electrode or the positiveelectrode, the effect is not changed.

When the active material for a battery according to the embodiment isused for a positive electrode, the active material for a negativeelectrode as the counter electrode thereof may be a metallic lithium, alithium alloy, or a carbonaceous material such as graphite or coke.

When the active material in the first embodiment is used as a positiveelectrode active material, the material may be used alone or togetherwith a different active material. Examples of other active materialsinclude lithium-titanium composite oxides having a spinel structure(Li₄Ti₅O₁₂, etc.), titanium composite oxides having an anatase-type,rutile-type, or monoclinic β-type structure (a-TiO₂, TiO₂(B) etc.), andiron composite sulfides (FeS and FeS₂ etc.). When the active material inthe first embodiment is used as a positive electrode active material,the material may be used alone or together with a different activematerial. Examples of other active materials include lithium-titaniumcomposite oxides having a spinel structure (Li₄Ti₅O₁₂ etc.), titaniumcomposite oxides having an anatase-type, rutile-type, or monoclinicβ-type structure (a-TiO₂, r-TiO₂, TiO₂(B) etc.), and iron compositesulfides (FeS and FeS₂ etc.).

When an electrode contains the different active material, the contentmay be measured as follows. The negative electrode active material takenout from the electrode is subjected to Transmission ElectronMicroscope-Energy Dispersive X-ray spectrometry (TEM-EDX), and thecrystal structure of each particle is specified by a selected areadiffraction method. A particle having a diffraction pattern belonging toa niobium composite oxide is selected so as to measure the carboncontent. At this time, the region of carbon existing can be known withcarbon mapping by EDX.

In the measurement with Fourier transform infrared spectrophotometer(FT-IR), the titanium composite oxide extracted in the same procedure isfixed onto a measuring tool, and then measured. For example, themeasurement can be made under the following conditions, using thefollowing apparatus:

Fourier transform type FTIR apparatus: FTS-60A (manufactured by BioRadDigilab Co.)

Light source: Special ceramic material

Detector: DTGS (Deuterium Tri-Glycine Sulfate)

Wavenumber resolving power: 4 cm⁻¹

Integration times: 256

Attached device: diffuse reflection measuring device (manufactured byPIKE Technologies Co.), aperture plate CaF₂

Reference: gold

The particle of the niobium composite oxide represented by the formulaLi_(x)M_((1-y))Nb_(y)Nb₂O_((7+δ)), that is, the primary particlepreferably have an average particle diameter of 10 nm to 100 μm. Whenthe average particle diameter of the primary particle is 10 nm or more,the oxide is easily handled in an industrial production. When theaverage particle diameter is 100 μm or less, lithium ions can besmoothly diffused in the solid of the niobium composite oxide.

Still more preferably, the average particle diameter is from 0.03 to 30μm. When the average particle diameter is 0.03 μm or more, the oxide iseasily handled in an industrial production. When the average particlediameter is 30 μm or less, the mass and the thickness of the electrodelayer are easily made uniform in the process of an electrode, andfurther the surface smoothness of the layer is improved.

The specific surface area of the active material is preferably from 0.5to 50 m²/g. When the specific surface area is 0.5 m²/g or more,adsorbing and eliminating sites for lithium ions can be sufficientlysecured. When the specific surface area is 50 m²/g or less, theparticles are easily handled in an industrial production thereof. Morepreferably, the specific surface area is from 3 to 30 m²/g.

(Production Process)

Subsequently, a process of producing the active material for a batteryof the first embodiment will be explained.

The process comprises obtaining the niobium composite oxide representedby the formula: Li_(x)M_((1-y))Nb_(y)Nb₂O_((7+δ)) in accordance with asolid phase reaction process and arranging carbonate ions on the surfacethereof.

First, the step of obtaining the niobium composite oxide represented bythe formula: Li_(x)M_((1-y))Nb_(y)Nb₂O_((7+δ)) will be explained.

First, starting materials are mixed. As the starting materials, oxidesoptionally containing Ti, Nb, and Zr or salts are used. In the synthesisof TiNb₂O₇, oxides such as titanium dioxide and niobium pentoxide may beused as the starting materials. The salts used as the starting materialsare preferably salts which decompose at relatively low temperatures toform oxides, like hydroxide salt, carbonate, and nitrate. Niobiumhydroxide and zirconium hydroxide are appropriate.

Next, the resultant mixture is ground and blended as uniformly aspossible. Then, the resultant mixture is sintered. The sintering can beperformed at a temperature range from 900 to 1400° C. for a total of 1hour to 100 hours.

The niobium composite oxide represented by the formula:Li_(x)M_((1-y))Nb_(y)Nb₂O_((7+δ)) can be obtained by the above steps.

It is acceptable that the lithium ions are inserted by the charging ofthe battery and remain, as irreversible capacity, in the activematerial. Alternatively, the active material may be synthesized as acomposite oxide containing lithium by using a compound containinglithium like lithium carbonate as a starting material. Therefore, theactive material may contain the monoclinic oxide phase represented bythe formula: Li_(x)M_((1-y))Nb_(y)Nb₂O_((7+δ)).

Subsequently, the step of arranging carbonate ions at least one part ofthe surface of the niobium composite oxide represented by the formula:Li_(x)M_((1-y))Nb_(y)Nb₂O_((7+δ)) obtained in the above step will beexplained.

In the step, the resultant niobium composite oxide is directly broughtinto contact with a carbonate ion containing solution or a hydroxidesalt containing solution. For example, the treatment is performed asfollows.

The niobium composite oxide represented by the formula:Li_(x)M_((1-y))Nb_(y)Nb₂O_((7+δ)), synthesized in the above step, wasadded to a predetermined amount of a solution of lithium carbonate(carbonate) or lithium hydroxide (hydroxide salt), which was stirred.The resultant solution is evaporated, for example, at 80° C. so that itis possible to obtain the niobium composite oxide represented by theformula: Li_(x)M_((1-y))Nb_(y)Nb₂O_((7+δ)) in which lithium carbonate orlithium hydroxide is arranged. The lithium hydroxide is converted intolithium carbonate in the air relatively immediately.

The niobium composite oxide in which carbonate ions are arranged ispreferably subjected to calcination. The calcination may be performed inthe air. The calcination conditions are as follows: temperature: 100 to600° C., preferably 300 to 450° C., time: 10 minutes to 100 hours,preferably 1 hour to 24 hours. The calcination is performed under suchconditions so that dense and adhesive carbonate ions can be attached.

Such treatment allows the niobium composite oxide represented by theformula: Li_(x)M_((1-y))Nb_(y)Nb₂O_((7+δ)) in which carbonate ions arearranged on at least one part of the surface to be obtained.

Hydroxide salt may be directly brought into contact with the carbondioxide gas before and after the reheat treatment so as to be convertedto carbonate ions.

According to the active material for a battery of the first embodimentproduced as described above, excellent charge/discharge cycleperformance is obtained.

(Measurement Method)

Hereinafter, various methods for measuring physical properties of theactive material for a battery of the first embodiment will be described.

<Wide-Angle X-Ray Diffraction Measurement>

The crystal structure of the active material can be detected by the wideangle X-ray diffraction (WAXD).

The wide-angle X-ray diffraction measurement of the active material isperformed as follows. First, a target sample is ground until the averageparticle diameter becomes about 5 μm or less or the particle size isselected with a sieve or the like. The average particle diameter can bedetermined by the laser diffractometry. In order to examine that thecrystallinity of the sample is not influenced by the grinding process,it is confirmed that the half width of the main peak does not changebefore and after the grinding process.

A holder portion with a depth of 0.2 mm or more formed on a glass sampleplate is filled with the ground sample, and the plane of the sample issmoothed using the glass plate. At this time, a further care must betaken to prevent the occurrence of cracks and voids caused by a lack ofthe sample to be filled. In order to properly determine the peakpositions, the filling is carried out so as to prevent the generation ofparts convexed or concaved from the standard level of the holder.

Then, the glass plate filled with the sample is placed in a wide-anglediffractometer and a diffraction pattern is obtained using Cu—Kα rays.

The influence of particle orientation may be caused depending on theparticle shape of the sample. The position of a peak may be shifted orthe intensity ratio may be changed. In this case, the same samples areput in a Lindeman glass capillary and measured using a rotating samplestage to examine the influence. Comparing the obtained X-ray charts, ifdifferences (beyond errors of the device) are found in the intensityratio of a specific surface, the measurement results using the rotatingsample stage are applied to the scope of right of the present invention.

When the wide-angle X-ray diffraction measurement is performed on theactive material contained in the electrode, it can be performed, forexample, as follows. In order to analyze the crystal state of the activematerial, the active material is put into a state in which lithium ionsare perfectly released from the active material. For example, when it isused as the negative electrode, the battery is put into a fullydischarged state. However, there is the case where lithium ions remaineven in a discharged state. In the wide-angle X-ray diffraction, it isdifficult to detect the presence of Li, however, it may appear as achange of the lattice constant. When Li is considered to remain in thecrystal structure, particular attention should be given to the resultsof analyses.

Next, the battery is disintegrated in a glove box filled with argon.Then, the electrode to be measured is washed with an appropriatesolvent. For example, it is preferable to use ethylmethyl carbonate orthe like. If the washing is insufficient, impurity phases such aslithium carbonate and lithium fluoride are mixed in due to the influenceof lithium ions remaining in the electrode. In that case, it ispreferable to use an airtight container in which the measurement isperformed in an inert gas atmosphere. Subsequently, the washed electrodeis cut into the same size as that of the area of the holder of thewide-angle diffractometer. The cut electrode is attached to the holderso as to be equal to the height of the standard level of the glassholder, followed by measurement. At this time, the position of the peakoriginated from the substrate is examined with regard to the kind of themetallic foil of the electrode substrate. The peak is subtracted fromthe measurement result. Further, the presence or absence of peaksoriginated from the ingredients such as a conductive agent and binder isexamined. Similarly, the peaks can be subtracted from the measurementresults. When the peak of the electrode substrate is overlapped on thepeak of the active material, it is desired to separate the activematerial from the substrate prior to the measurement. This is necessaryto accurately measure the peak intensity. The electrode is immersed in asolvent such as ethylmethyl carbonate and ultrasonic waves are appliedthereto so that the electrode can be separated from the substrate.Thereafter, the electrode powder (including the active material, theconductive assistant, and the binder) which is recovered by volatilizingthe solvent is put in a Lindeman glass capillary and subjected to thewide-angle X-ray diffraction measurement. Further, the electrode powderrecovered in the same manner as described above may be subjected tovarious chemical analyses.

The results of the WAXD obtained in this manner are analyzed by theRietveld method. In the Rietveld method, a diffraction pattern iscalculated from a crystal structure model assumed in advance. Then, thediffraction pattern is fully fitted to actual values so as to improvethe accuracy of parameters (for example, lattice constant, atomiccoordination and occupation) relating to the crystal structure.Therefore, the characteristics of the crystal structure of thesynthesized material can be investigated.

<Confirmation of Content of Element>

The content of the element can be measured by Inductively Coupled Plasma(ICP) emission spectrometry. The measurement of the elemental content byICP emission spectrometry can be executed, for example, in the followingmanner. A battery is disassembled in a discharge state, and an electrode(e.g., a negative electrode) is taken out, followed by deactivation ofthe active material containing layer in water. Thereafter, the activematerial contained in the active material containing layer is extracted.The extraction treatment may be performed by removing a conductive agentand a binder in the active material containing layer by a heat treatmentin air, for example. After transferring the extracted active material toa container, acid fusion or alkali fusion is performed to obtain ameasurement solution. ICP emission spectroscopy of the measurementsolution is conducted by using a measurement apparatus (e.g., SPS-1500V,manufactured by SII Nanotechnology Inc.) to measure the elementalcontent.

It is acceptable that the active material according to the embodimentcontains 1000 mas ppm or less of inevitable impurities in production, inaddition to the elements described in the present invention.

<Confirmation of Solid State>

The state of the crystal phase is confirmed by wide angle X-raydiffraction analysis so that it is possible to determine whether theadded element M is substituted and dissolved. Specifically, the presenceof impurity phases, changes in lattice constant (the ionic radius of theadded element is reflected) or the like can be determined. However, whenit is added in a small amount, some cases cannot be determined by thesemethods. At that time, the distribution state of the added element canbe found by observation with the Transmission Electron Microscope (TEM)and measurement with the Electron Probe Micro Analyzer (EPMA).Accordingly, it is possible to determine whether the added element isuniformly distributed in a solid or segregated.

<Particle Diameter and BET Specific Surface Area>

The average particle diameter of the active material is not particularlylimited and it may be changed according to desired batterycharacteristics. The BET specific surface area of the active material isnot particularly limited and it is preferably 0.5 m²/g or more and lessthan 50 m²/g. If the specific surface area is 0.5 m²/g or more, thenecessary contact area with the nonaqueous electrolyte can be ensured.Thus, excellent discharge rate performance is easily obtained. Further,the charging time can be reduced. On the other hand, if the specificsurface area is less than 50 m²/g, the reactivity with the nonaqueouselectrolyte does not become too high, and lifetime characteristics canbe improved. In the process of producing an electrode, coatingproperties of a slurry containing the active material can be improved.

The specific surface area is measured using a method in which moleculeswhose adsorption occupied area is known are allowed to adsorb to theplane of powder particles at the temperature of liquid nitrogen to findthe specific surface area of the sample from the amount of the adsorbedmolecules. The most frequently used method is a BET method based on thelow temperature/low humidity physical adsorption of an inert gas. TheBET method is a famous theory as a calculation method of the specificsurface area in which the Langmuir theory as a monolayer adsorptiontheory is extended to multilayer adsorption. The specific surface areadetermined by the BET method is called “BET specific surface area”.

Second Embodiment

A nonaqueous electrolyte battery according to the second embodiment willbe described.

The nonaqueous electrolyte battery of the second embodiment includes apositive electrode, a negative electrode containing the active materialfor a battery of the first embodiment, and a nonaqueous electrolyte. Thenonaqueous electrolyte battery of the second embodiment may include acase. In this case, the nonaqueous electrolyte battery comprises thecase, the positive electrode housed in the case, the negative electrodewhich is spatially apart from the positive electrode in the case in sucha manner that, for example, a separator is interposed between theelectrodes, and the nonaqueous electrolyte filled in the case.

An example of the nonaqueous electrolyte battery 100 according to theembodiment will be explained more in detail with reference to FIGS. 3and 4. FIG. 3 is a cross-sectional view of the flat type nonaqueouselectrolyte battery 100 with an case 2 formed of a laminate film. FIG. 4is an enlarged sectional view of an A portion of FIG. 3. The figures areeach a schematic view referred to in order to describe the battery. Theshape and the sizes of each member therein, the ratio between some ofthe sizes, and others may be different from those in an actual form ofthe device; however, these may be appropriately changed with referencethe following description and any known technique.

A flat wound electrode group 1 is housed in a baggy case 2 formed of alaminated film in which an aluminum foil is intervened between two resinlayers. The flat wound electrode group 1 is formed by winding, into aspiral form, a laminate wherein a negative electrode 3, a separator 4, apositive electrode 5 and another separator 4 are laminated so as to bepositioned in this order from the outside, and then press-forming thewound laminate. As illustrated in FIG. 4, the outmost moiety of thenegative electrode 3 has a structure wherein a negative electrode layer3 b is formed on the inside surface of a negative electrode currentcollector 3 a. The other moieties of the negative electrode 3 each havea structure wherein negative electrode layers 3 b are formed on bothsurfaces of the negative electrode current collector 3 a, respectively.An active material in the negative electrode layer 3 b contains theactive material for a battery according to the first embodiment. Thepositive electrode 5 has a structure wherein positive electrode layers 5b are formed on both surfaces of a positive electrode current collector5 a, respectively.

Near the outer circumferential end of the wound electrode group 1, anegative electrode terminal 6 is connected electrically to the negativeelectrode current collector 3 a of the outermost moiety of the negativeelectrode 3, and a positive electrode terminal 7 is connectedelectrically to the positive electrode current collector 5 a of theinside positive electrode 5. The negative electrode terminal 6 and thepositive electrode terminal 7 are extended outwardly from an openingpart of the baggy case 2. For example, the liquid nonaqueous electrolyteis injected from the opening part of the baggy case 2. The woundelectrode group 1 and the liquid nonaqueous electrolyte can becompletely sealed by heat-sealing the opening part of the baggy case 2across the negative electrode terminal 6 and the positive electrodeterminal 7.

For the negative electrode terminal 6, use is made of, for example, amaterial having electroconductivity, and electrical stability when thematerial is at a potential of 1 V to 3 V relative to metallic lithiumions. A specific example thereof is aluminum, or an aluminum alloycontaining Mg, Ti, Zn, Mn, Fe, Cu, Si or some other element. The rawmaterial of the negative electrode terminal 6 is preferably equivalentto that of the negative electrode current collector 3 a in order todecrease the contact resistance between the negative electrode terminal6 and the negative electrode current collector 3 a.

For the positive electrode terminal 7, use is made of, for example, amaterial having electroconductivity, and electrical stability when thematerial is at a potential of 3 to 4.25 V relative to metallic lithiumions. A specific example thereof is aluminum, or an aluminum alloycontaining Mg, Ti, Zn, Mn, Fe, Cu, Si or some other element. The rawmaterial of the positive electrode terminal 7 is preferably equivalentto that of the positive electrode current collector 5 a in order todecrease the contact resistance between the positive electrode terminal7 and the positive electrode current collector 5 a.

The case 2, a negative electrode 3, a positive electrode 5, a separator4, and the nonaqueous electrolyte, which are constituting members of thenonaqueous electrolyte battery 100, will be explained in detail.

1) Case

The case 2 is formed of a laminated film having a thickness of 0.5 mm orless. Alternatively, as the case, a metallic vessel having a thicknessof 1.0 mm or less is used. The thickness of the metallic vessel ispreferably 0.5 mm or less.

The shape of the case 2 can be selected from the flat type (thin type),rectangular type, cylindrical type, coin type, and button type. Examplesof the case include a case for a small battery which is loaded into aportable electronic device or a case for a large battery which is loadedinto a two- or four-wheeled vehicle depending on the size of thebattery.

For the laminated film, use is made of a multi-layered film wherein ametal layer is interposed between any two of resin layers. The metallayer is preferably an aluminum foil or aluminum alloy foil in order toreduce the weight. The resin layers may each be, for example, a layer ofa polymeric material such as polypropylene (PP), polyethylene (PE),nylon, or polyethylene terephthalate (PET). The laminated film can beformed into a shape of the case by heat sealing.

The metallic vessel may be made of aluminum, an aluminum alloy or thelike. It is preferable that the aluminium alloy includes elements suchas Mg, Zn, and Si. When transition metals such as Fe, Cu, Ni, and Cr arecontained in the alloy, the content is preferably 100 mass ppm or less.

2) Negative Electrode

The negative electrode 3 comprises the current collector 3 a, and thenegative electrode layer 3 b, which is formed on a single surface oreach surface of the current collector 3 a to contain an active material,a conductive agent and a binder.

The active material for a battery according to the first embodiment isused as the active material.

The nonaqueous electrolyte battery 100, into which the negativeelectrode 3 having the negative electrode layer 3 b containing theactive material is integrated, has a high-current property and anexcellent charge/discharge cycle performance.

The conductive agent makes the current collecting performance of theactive material high, and restrains the contact resistance between theactive material and the current collector. Examples of the conductiveagent include acetylene black, carbon black and graphite.

The binder makes it possible to bind the active material and theconductive agent to each other. Examples of the binder includepolytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF),fluorine-contained rubber, and styrene butadiene rubber.

In the negative electrode layer 3 b, the active material, the conductiveagent and the binder are preferably blended at a ratio of 70% to 96% bymass, a ratio of 2% to 28% by mass, and a ratio of 2% to 28% by mass,respectively. When the ratio of the conductive agent is set to 2% ormore by mass, the current collecting performance of the negativeelectrode layer 3 b is improved, so that the high-current characteristicof the nonaqueous electrolyte battery 100 can be improved. When theratio of the binder is set to 2% or more by mass, the bindingperformance between the negative electrode layer 3 b and the currentcollector 3 a is made high, so that the cycle characteristic can beimproved. When the ratios of the conductive agent and the binder areeach set to 28% or less by mass, the capacity of the battery can befavorably made high.

The current collector 3 a is preferably an aluminum foil piece, which iselectrochemically stable in the potential range of 1 V or higher, or analuminum alloy foil piece containing Mg, Ti, Zn, Mn, Fe, Cu, Si or someother element.

The negative electrode 3 is formed, for example, by suspending theactive material, the conductive agent, and the binder into a widelyusable solvent to prepare a slurry, painting the slurry onto the currentcollector 3 a, drying the painted slurry, and then pressing the driedfilm. The negative electrode 3 may be formed by making the activematerial, the conductive agent and the binder into a pellet form, andforming the pellets into the negative electrode layer 3 b onto thecurrent collector 3 a.

3) Positive Electrode

The positive electrode 5 comprises the current collector 5 a, and thepositive electrode layer 5 b, which is formed on a single surface oreach surface of the current collector 5 a to contain an active material,a conductive agent and a binder. The active material may be, forexample, an oxide or a polymer.

Usable examples of the oxide include manganese dioxide absorbing lithium(MnO₂), iron oxide, copper oxide, and nickel oxide, and lithiummanganese composite oxides (e.g., Li_(x)Mn₂O₄ or Li_(x)MnO₂), lithiumnickel composite oxides (e.g., Li_(x)NiO₂), lithium cobalt compositeoxides (Li_(x)CoO₂), lithium nickel cobalt composite oxides (e.g.,LiNi_(1-y)Co_(y)O₂), lithium manganese cobalt composite oxides (e.g.,Li_(x)MnyCo_(1-y)O₂), lithium manganese nickel composite oxides having aspinel structure (Li_(x)Mn_(2-y)Ni_(y)O₄), lithium phosphorus oxideshaving an olivine structure (e.g., Li_(x)FePO₄, Li_(x)Fe_(1-y)Mn_(y)PO₄,and Li_(x)CoPO₄), iron sulfate (Fe₂(SO₄)₃), and vanadium oxides (e.g.,V₂O₅). Here, x and y are preferably 0<x≦1 and 0≦y≦1, respectively.

The polymer may be, for example, a conductive polymer such aspolyaniline or polypyrrole, or a disulfide-based polymer material. Theactive material may be sulfur (S) or carbon fluoride.

Examples of a preferred active material include a lithium manganesecomposite oxide having a high positive electrode voltage (Li_(x)Mn₂O₄),a lithium nickel composite oxide (Li_(x)NiO₂), a lithium cobaltcomposite oxide (Li_(x)CoO₂), a lithium nickel cobalt composite oxide(Li_(x)Ni_(1-y)Co_(y)O₂), a lithium-manganese-nickel composite oxidehaving a spinel structure (Li_(x)Mn_(2-y)Ni_(y)O₄), a lithium manganesecobalt composite oxide (Li_(x)Mn_(y)Co_(1-y)O₂), and lithium ironphosphate (Li_(x)FePO₄). Here, x and y are preferably 0<x≦1 and 0≦y≦1,respectively.

The active material is more preferably a lithium cobalt composite oxideor a lithium manganese composite oxide. The active material is high inion conductivity; thus, in any combination of the active material withthe above-mentioned negative electrode active material, the diffusion oflithium ions in the positive electrode active material does not become arate-determining step easily. Therefore, the active material isexcellent in adaptability to the lithium titanium composite oxide in thenegative electrode active material.

The conductive agent makes the current collecting performance of theactive material high, and restrains the contact resistance between theactive material and the current collector. Examples of the conductiveagent include carbonaceous materials such as acetylene black, carbonblack and graphite.

The binder makes it possible to bind the active material and theconductive agent to each other. Examples of the binder includepolytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), andfluorine-contained rubber.

In the positive electrode layer 5 b, the active material, the conductiveagent and the binder are preferably blended at a ratio of 80% to 95% bymass, a ratio of 3% to 18% by mass, and a ratio of 2% to 17% by mass,respectively. When the ratio of the conductive agent is set to 3% ormore by mass, the above-mentioned advantageous effects can be produced.When the ratio of the conductive agent is set to 18% or less by mass,the decomposition of the nonaqueous electrolyte on the surface of theconductive agent can be decreased when the battery is stored at hightemperature. When the ratio of the binder is set to 2% or more by mass,a sufficient positive electrode strength can be obtained. When the ratioof the binder is set to 17% or less by mass, the blend ratio of thebinder, which is an insulating material, in the positive electrode isdecreased so that the internal resistance can be decreased.

The current collector is preferably, for example, an aluminum foilpiece, or an aluminum alloy foil piece containing Mg, Ti, Zn, Mn, Fe,Cu, Si or some other element.

The positive electrode 5 is formed, for example, by suspending theactive material, the conductive agent, and the binder into a widelyusable solvent to prepare a slurry, painting the slurry onto the currentcollector 5 a, drying the painted slurry, and then pressing the driedfilm. The positive electrode 5 may be formed by making the activematerial, the conductive agent and the binder into a pellet form, andforming the pellets into the positive electrode layer 5 b onto thecurrent collector 5 a.

4) Nonaqueous Electrolyte

The nonaqueous electrolyte may be, for example, a liquid nonaqueouselectrolyte prepared by dissolving an electrolyte into an organicsolvent, or a gel-form nonaqueous electrolyte wherein a liquidelectrolyte and a polymeric material are compounded with each other.

About the liquid nonaqueous electrolyte, an electrolyte is preferablydissolved into an organic solvent to give a concentration of 0.5 M to2.5 M.

Examples of the electrolyte include lithium perchlorate (LiClO₄),lithium hexafluorophosphate (LiPF₆), lithium tetrafluoroborate (LiBF₄),lithium hexafluoroarsenate (LiAsF₆), lithium trifluorometasulfonate(LiCF₃SO₃), a lithium salt of lithium bistrifluoromethylsulfonylimide[LiN(CF₃SO₂)₂], and mixtures of two or more thereof. The electrolyte ispreferably an electrolyte which is not easily oxidized at a highpotential, and is most preferably LiPF₆.

Examples of the organic solvent include cyclic carbonates such aspropylene carbonate (PC), ethylene carbonate (EC) and vinylenecarbonate; linear carbonates such as diethyl carbonate (DEC), dimethylcarbonate (DMC) and methyl ethyl carbonate (MEC); cyclic ethers such astetrahydrofuran (THF), 2-methyltetrahydrofuran (2MeTHF) and dioxolane(DOX); linear ethers such as dimethoxyethane (DME) and diethoxyethane(DEE); g-butyrolactone (GBL); acetonitrile (AN); and sulfolane (SL).These organic solvents may be used alone or in the form of a mixture.

Examples of the polymeric material include polyvinylidene fluoride(PVdF), polyacrylonitrile (PAN), and polyethylene oxide (PEO).

The organic solvent is preferably a mixed solvent made of at least twoselected from the group consisting of propylene carbonate (PC), ethylenecarbonate (EC) and diethyl carbonate (DEC), or a mixed solventcontaining g-butyrolactone (GBL). By use of the mixed solvent, anonaqueous electrolyte battery excellent in high-temperature propertycan be obtained.

5) Separators

The separators 4 may each be, for example, a porous film containingpolyethylene, polypropylene, cellulose or polyvinylidene fluoride(PVdF), or a nonwoven cloth made of a synthetic resin. The porous filmis preferably made of polyethylene or polypropylene. Since the film ismelted at a predetermined temperature to make it possible to block anelectric current, safety can be improved.

According to the second embodiment, it can be provided a nonaqueouselectrolyte battery having excellent charge/discharge cycle performance.

Third Embodiment

Subsequently, a battery pack according to the third embodiment will beexplained in detail.

The battery pack according to the third embodiment has one or more ofthe nonaqueous electrolyte batteries (that is, unit cells) according tothe second embodiment. When a plurality of unit cells are contained inthe battery pack, each of the unit cells is electrically connected inseries or in parallel, or in series and in parallel, and arranged.

A battery pack 200 will be specifically described with reference toFIGS. 5 and 6. In the battery pack 200 shown in FIG. 5, the nonaqueouselectrolyte battery shown in FIG. 3 is used as unit cells 21.

The unit cells 21 are laminated onto each other in such a manner thattheir negative electrode terminals 6 and positive electrode terminals 7,which are extended to the outside, are arranged into the same direction,and further the unit cells 21 are fastened onto each other through anadhesive tape 22 to constitute a battery module 23. As illustrated inFIG. 6, these unit cells 21 are connected electrically to each other inseries.

A printed wiring board 24 is arranged opposed to the side plane of theunit cells 21 where the negative electrode terminal 6 and the positiveelectrode terminal 7 are extended. A thermistor 25, a protective circuit26, and an energizing terminal 27 to an external instrument are mountedon the printed wiring board 24 as shown in FIG. 6. An electricinsulating plate (not shown) is attached to the surface of the printedwiring board 24 facing the battery module 23 to avoid unnecessaryconnection of the wiring of the battery module 23.

A positive electrode side lead 28 is connected to the positive electrodeterminal 7 positioned as the lowest layer of the battery module 23, andthe tip thereof is inserted into a positive electrode side connector 29of the printed wiring board 24 to be connected electrically thereto. Anegative electrode side lead 30 is connected to the negative electrodeterminal 6 positioned as the highest layer of the battery module 23, andthe tip thereof is inserted into a negative electrode side connector 31of the printed wiring board 24 to be connected electrically thereto. Theconnectors 29 and 31 are connected to the protective circuit 26 throughwirings 32 and 33 formed in the printed wiring board 24.

The thermistor 25 is used to detect the temperature of the unit cells21. A signal of the detection is transmitted to the protective circuit26. The protective circuit 26 can shut down a plus-side wiring 34 a anda minus-side wiring 34 b between the protective circuit 26 and theenergizing terminals 27 energizing an external instrument under apredetermined condition. The predetermined condition is, for example, atime when the detected temperature of the thermistor 25 reaches apredetermined temperature or is higher than the temperature. Thepredetermined condition is also a time when an overcharge, anoverdischarge or an overcurrent of the unit cells 21, or some other isdetected. The overcharge detection may be performed on each of the unitcells 21 or the whole of the unit cells 21. When each of the unit cells21 is detected, the cell voltage may be detected, or positive electrodeor negative electrode potential may be detected. In the latter case, alithium electrode used as a reference electrode is inserted into theindividual unit cells 21. In the case of FIGS. 5 and 6, wirings 35 forvoltage detection are connected to the unit cells 21 and detectionsignals are sent to the protective circuit 26 through the wirings 35.

Protective sheets 36 comprised of rubber or resin are arranged on threeside planes of the battery module 23 except the side plane in which thepositive electrode terminal 7 and the negative electrode terminal 6 areprotruded.

The battery module 23 is housed in a holder 37 together with each of theprotecting sheets 36 and the printed wiring board 24. In other words,the respective protecting sheets 36 are arranged onto the two inner sidefaces of the holder 37 along the holder long-side direction and one oftwo inner side faces of the holder 37 along the holder short-sidedirection, and further the printed wiring board 24 is arranged onto theother inner side face along the holder short-side direction. The batterymodule 23 is located in a space surrounded by the protecting sheets 36and the printed wiring board 24. A cover 38 is fitted to the uppersurface of the holder 37.

For the fixing of the battery module 23, a thermally shrinkable tape maybe used instead of the adhesive tape 22. In this case, protecting sheetsare arranged on two side faces of the battery module, respectively, andthe thermally shrinkable tape is wound around the battery module, andthen the tape is thermally shrunken to bind the battery modules to eachother.

In FIGS. 5 and 6, the form in which the unit cells 21 are connected inseries is shown. However, in order to increase the battery capacity, thecells may be connected in parallel. Alternatively, the cells may beformed by combining series connection and parallel connection. Theassembled battery pack can be connected in series or in parallel.

According to the third embodiment, the nonaqueous electrolyte batteryhaving excellent charge/discharge cycle performance in the secondembodiment is included so that a battery pack having excellentcharge/discharge cycle performance can be provided.

The form of the battery pack may be appropriately changed in accordancewith the usage thereof. The battery pack is preferably used for anarticle exhibiting an excellent charge/discharge cycle performance whena large current is taken out therefrom. Specifically, the pack is usedfor, for example, a power source of a digital camera, a hybrid electrictwo- to four-wheeled vehicle, an electric two- to four-wheeled vehicle,an assisting bicycle, or some other vehicle. In particular, the batterypack of the embodiment wherein a nonaqueous electrolyte batteryexcellent in high-temperature property is used is preferably used for avehicle.

Fourth Embodiment

A vehicle according to the fourth embodiment comprises the battery packaccording to the third embodiment. Examples of the vehicle referred toherein include hybrid electric two- to four-wheeled vehicles, electrictwo- to four-wheeled vehicles, and assisting bicycles.

An example of the fourth embodiment includes a hybrid type vehicle usinga running power source which is produced by combination of an internalcombustion engine and an electromotor drivable by a battery. For thedriving power of any vehicle, a driving power for widely-extendablerotation number and torque is required depending on the runningconditions. In general, the torque and the rotation number which exhibitideal energy efficiency are restricted in the internal combustionengines. Thus, under other torques and the rotation numbers, the energyefficiency is lowered. Hybrid type vehicles each have a characteristicthat its internal combustion engine is driven under optimum conditionsto generate electric power and further its wheels are driven by a highlyefficient electromotor, or the dynamic power of its internal combustionengine and that of its electromotor are combined with each other todrive the wheels, whereby the energy efficiency of the whole of thevehicle can be improved. Moreover, when the speed of the vehicledecreases, the kinetic energy of the vehicle is converted so as to beregenerated as electric power, whereby the mileage thereof can begreatly increased from that of ordinary vehicles drivable by theirinternal combustion engine alone.

Hybrid vehicles can be roughly classified into three types in accordancewith the combination of their internal combustion engine with theirelectromotor.

The first type is a hybrid vehicle which is generally called a serieshybrid car. All of the dynamic power of an internal combustion engine isonce converted to an electric power through a power source. Thiselectric power is stored in a battery pack through an inverter. As thisbattery pack, the battery pack according to the third embodiment can beused. The electric power of the battery pack is supplied through theinverter to an electromotor. The electromotor drives wheels. This systemis a system wherein a power source is hybridized with an electricvehicle. Its internal combustion engine can be driven under a drivingcondition for high efficiency, and further kinetic energy can beconverted into electric power. However, the wheels are driven by onlythe electromotor, so that a high-power electromotor is required as theelectromotor. Additionally, the battery pack is required to have arelatively large capacity. The rated capacity of the battery pack isdesirably set into the range of 5 to 50 Ah. The capacity is moredesirably in the range of 10 to 20 Ah. The rated capacity referred toherein means the capacity of the battery pack when the pack isdischarged at a rate of 0.2 C.

The second type is a hybrid vehicle which is generally called a parallelhybrid car. The hybrid vehicle has an electromotor which functions alsoas a power source. An internal combustion engine mainly drives wheels.As the case may be, a part of the dynamic force thereof is applied tothe electromotor to be converted to an electric power. By use of theelectric power, a battery pack is charged. At the time of the start oracceleration of the vehicle, when a large load is applied to theinternal combustion engine, driving force is assisted by theelectromotor. The base of the vehicle is an ordinary vehicle, and thepresent system is a system wherein a variation in the load onto theinternal combustion engine is made small to attain a high efficiency,and the conversion of kinetic energy to electric power and others aretogether conducted. The wheels are driven mainly by the internalcombustion engine, so that the output power of the electromotor can bedecided at will by the percentage of a necessary assist. Even if anelectromotor and battery pack having a relatively small size are used,the system can be configured. The rated capacity of the battery pack maybe in the range of 1 to 20 Ah. The capacity is more desirably in therange of 5 to 10 Ah.

The third type is a hybrid vehicle which is generally called a seriesparallel hybrid car. This hybrid vehicle is a type of combining a serieshybrid with a parallel hybrid. It includes a dynamic force dividingmechanism. The mechanism divides the output power of an internalcombustion engine into a power for generating electric power and a powerfor driving wheels. This type makes it possible to control load onto theengine minuter than the parallel type to make the energy efficiencyhigher.

The rated capacity of the battery pack is desirably set into the rangeof 1 to 20 Ah. The capacity is more desirably in the range of 5 to 10Ah.

The nominal voltage of the battery pack mounted on each of the threetype hybrid vehicles is desirably in the range of 200 to 600 V.

In general, each of the battery packs is preferably arranged in a spacewhich has a temperature that is not easily affected by a change in thetemperature of the outside air and does not easily receive any impactwhen the vehicle collides or undergoes some other accident. For example,in a sedan, the battery pack may be arranged inside a trunk room behinda rear sheet. The battery pack may be arranged under or behind thesheet. When the mass of the battery is large, it is preferred to arrangethe battery under the sheet or the other sheet or below the floor inorder to make the gravity center of the vehicle low.

According to the fourth embodiment, when the battery pack excellent incycle characteristics according to the third embodiment is included, avehicle having excellent performance can be provided.

The embodiment of the present invention has been hereinabove explained.However, this embodiment is presented as an example, and is not intendedto limit the scope of the invention. These new embodiments can beembodied in various other forms, and various kinds of omissions,replacements, and changes can be made without deviating from the gist ofthe invention. These embodiments and the modifications thereof areincluded in the scope and the gist of the invention, and are included inthe invention described in the claims and the scope equivalent thereto.

EXAMPLE Example 1 Synthesis of Niobium Composite Oxide

Titanium dioxide (TiO₂) having an anatase structure was mixed withniobium pentoxide (Nb₂O₅). The mixture was sintered at 1100° C. for 24hours to obtain a niobium composite oxide of the composition formulaTiNb₂O₇ (sample A1).

The fact that the resultant substance was a niobium composite oxiderepresented by the composition formula: TiNb₂O₇ was confirmed by thewide angle X-ray diffraction method described below. The BET specificsurface area of the substance was 10.2 m²/g and the pH was 6.9.

Next, 100 g of the niobium composite oxide (sample A1) of thecomposition formula: TiNb₂O₇ was added to 100 g of water containing 3 gof lithium hydroxide dissolved therein. The mixture was left alone in adesiccator at 70° C. while stirring it to evaporate the moisture.Thereafter, the resultant product was heated in air at 400° C. for 3hours to obtain a sample B1. The specific surface area of the sample B1was 9.6 m²/g and the pH was 8.7.

<Wide Angle X-Ray Diffraction Method>

The resultant titanium composite oxide was filled into a standard glassholder having a diameter of 25 mm, and then the oxide was measured by awide angle X-ray diffraction method. As a result, an X-ray diffractionpattern shown in FIG. 10 was obtained. From this diffraction pattern, itwas confirmed that a main substance constituting the resultant titaniumcomposite oxide was a monoclinic niobium composite oxide represented bythe composition formula: TiNb₂O₇ belonging to 39-1407 according to JCPDS(Joint Committee on Powder Diffraction Standards). The devices andconditions used for the measurement are shown as follows:

(1) X-ray generator: RU-200R, manufactured by Rigaku Corporation(Rotating anti-cathode type)

X-ray source: CuKα rays

Curved crystal monochromator (using graphite)

Power: 50 kV, 200 mA

(2) Goniometer: 2155S2 type, manufactured by Rigaku Corporation

Slit system: 1°-1°-0.15 mm-0.45 mm

Detector: Scintillation counter

(3) Count recorder: RINT1400 type, manufactured by Rigaku Corporation

(4) Scanning manner: 2θ/θ continuous scanning

(5) Qualitative analysis

Measurement range (2θ) 5 to 100°

Scanning speed: 2°/min

Step width (2θ) 0.02°

<Carbon Content>

The carbon content of the resultant titanium composite oxide (sample B1)was measured by the infrared absorption method. As a result, it wasconfirmed that the content was be 0.12% by mass.

<Production of Electrode>

A slurry was prepared by adding 90% by mass of powder of the titaniumcomposite oxide (sample B1) obtained as an active material, 5% by massof acetylene black as a conductive agent, and 5% by mass ofpolyvinylidene fluoride (PVdF) to N-methylpyrrolidone (NMP) and mixing.The slurry was applied on both surfaces of a current collector made froman aluminum foil having a thickness of 12 μm, followed by drying.Thereafter, a negative electrode having an electrode density of 2.8g/cm³ was obtained by pressing.

<Preparation of Liquid Nonaqueous Electrolyte>

Ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at avolume ratio of 1:2 to obtain a mixed solvent. LiPF₆ as an electrolytewas at a concentration of 1M at a concentration of 1M in the mixedsolvent to prepare a liquid nonaqueous electrolyte.

<Production of Beaker Cells>

The produced electrode was used as a working electrode. A beaker cell inwhich lithium metal was used as a counter electrode and a referenceelectrode was produced. The liquid nonaqueous electrolyte was injectedto complete a beaker cell of Example 1.

Comparative Example 1

In the production method described in Example 1, as the active material,the sample A1 was used in place of the sample B1 to produce a beakercell of Comparative example 1.

Examples 2 to 7 and Comparative Example 2

In the production method described in Example 1, the amount of lithiumhydroxide of a lithium hydroxide solution was changed to produce varioussamples (TiNb₂O₇) (samples C1 to I1). Specifically, the amount of thelithium hydroxide to be added to 100 g of water was as follows: 0.5 gfor the sample C1, 1 g for the sample D1, 2 g for the sample B1, 4 g forthe sample F1, 5 g for the sample G1, 10 g for the sample H1, and 20 gfor the sample I1.

The resultant substance was measured by the wide angle X-ray diffractionmethod in the same manner as Example 1. As a result, it was identifiedthat the sample was a monoclinic niobium composite oxide (space group:C/2m) belonging to No. 39-1407 according to the JCPDS card, representedby the formula: Li_(x)M_((1-y))Nb_(y)Nb₂O_((7+δ)).

The carbon content and pH of the samples C1 to I1 were measured in thesame manner as Example 1. These results are shown in Table 1.

A beaker cell was produced in the same manner as Example 1 using any ofthe samples C1 to I1 as the active material (respectively, Examples 2 to7 and Comparative example 2).

Example 8

In the production method described in Example 1, a lithium carbonatesolution prepared by dissolving 4.6 g of lithium carbonate in 100 g ofwater was used in place of the lithium hydroxide solution to produce asample J1 (TiNb₂O₇).

The resultant substance was measured by the wide angle X-ray diffractionmethod in the same manner as Example 1. As a result, it was identifiedthat the sample was a monoclinic niobium composite oxide (space group:C/2m) belonging to No. 39-1407 according to the JCPDS card, representedby the formula: Li_(x)M_((1-y))Nb_(y)Nb₂O_((7+δ)).

The specific surface area of the sample J1 was 9.7 m²/g and the pH was8.5.

A beaker cell was produced in the same manner as Example 1 using thesample J1 as the active material (Example 8).

Example 9

Titanium dioxide having an anatase structure (TiO₂), niobium pentoxide(Nb₂O₅), and zirconium dioxide (ZrO₂) were mixed. The mixture wassintered at 1100° C. for 24 hours to obtain a niobium composite oxide(Ti_(0.9)Zr_(0.1)Nb₂O₇) (sample A2). The particle size was adjusted bydry-milling using zirconia balls. The pH of the substance was 6.9.

Next, 100 g of the niobium composite oxides (sample A2) of thecomposition formula: Ti_(0.8)Zr_(0.2)Nb₂O₇ was added to 100 g of watercontaining 3 g of lithium hydroxide dissolved therein. The mixture wasleft alone in a desiccator at 70° C. while stirring it to evaporate themoisture. Thereafter, the resultant product was heated in air at 400° C.for 3 hours to obtain a sample B2. The pH of the sample B2 was 8.6.

The sample was measured by the wide angle X-ray diffraction method inthe same manner as Example 1. As a result, it was confirmed that thesample was a monoclinic niobium composite oxide (space group: C/2 m)belonging to No. 39-1407 according to the JCPDS card, represented by theformula: Li_(x)M_((1-y))Nb_(y)Nb₂O_((7+δ)).

The carbon content of the obtained titanium oxide was measured by theinfrared absorption method. As a result, it was confirmed that thecarbon content contained in the sample B2 was 0.12% by mass.

A beaker cell was produced in the same manner as Example 1 using thesample B2 as the active material (Example 9).

Comparative Example 3

A beaker cell was produced in the same manner as Example 1 using thesample A2 as the active material (Comparative example 3).

Example 10

Titanium dioxide (TiO₂) having an anatase structure and niobiumpentoxide (Nb₂O₅) were mixed. The mixture was sintered at 1100° C. for24 hours to produce a niobium composite oxide (Ti_(0.9)Nb_(2.1)O_(7.05))(sample A3). The particle size was adjusted by dry-milling usingzirconia balls. The pH of the substance was 7.0.

Next, 100 g of the niobium composite oxides (sample A3) of thecomposition formula: Ti_(0.9)Nb_(2.1)O_(7.05) was added to 100 g ofwater containing 3 g of lithium hydroxide dissolved therein. The mixturewas left alone in a desiccator at 70° C. while stirring it to evaporatethe moisture. Thereafter, the resultant product was heated in air at400° C. for 3 hours to obtain a sample B3. The pH of the sample B3 was9.0.

The sample was measured by the wide angle X-ray diffraction method inthe same manner as Example 1. As a result, it was confirmed that thesample was a monoclinic niobium composite oxide (space group: C/2 m)belonging to No. 39-1407 according to the JCPDS card, represented by theformula: Li_(x)M_((1-y))Nb_(y)Nb₂O_((7+δ)).

The carbon content of the obtained titanium oxide was measured by theinfrared absorption method. As a result, it was confirmed that thecarbon content contained in the sample B2 was 0.13 by mass.

A beaker cell was produced in the same manner as Example 1 using thesample B3 as the active material (Example 10).

Comparative Example 4

A beaker cell was produced in the same manner as Example 1 using thesample A3 as the active material (Comparative example 4).

Example 11

Niobium hydroxide (Nb(OH)₅) was sintered at 1100° C. for 24 hours toobtain a niobium oxide (M-Nb₂O₅) (sample A4). Further, the dry-millingof the resulting product was carried out using zirconia balls. The pH ofthe substance was 7.1.

Next, 100 g of the niobium composite oxides (sample A4) of thecomposition of M-Nb₂O₅ was added to 100 g of water containing 3 g oflithium hydroxide dissolved therein. The mixture was left alone in adesiccator at 70° C. while stirring it to evaporate the moisture.Thereafter, the resultant product was heated in air at 400° C. for 3hours to obtain a sample B4. The pH of the sample B4 was 9.8.

The sample was measured by the wide angle X-ray diffraction method inthe same manner as Example 1. As a result, it was identified that thesample was a monoclinic niobium oxide (space group: P12/m1) belonging toNo. 27-1313 according to the JCPDS card, represented by the formula:Li_(x)M_((1-y))Nb_(y)Nb₂O_((7+δ)).

The carbon content of the obtained titanium oxide was measured by theinfrared absorption method. As a result, it was confirmed that thecarbon content contained in the sample B4 was 0.19% by mass.

A beaker cell was produced in the same manner as Example 1 using thesample B4 as the active material (Example 11).

Comparative Example 5

A beaker cell was produced in the same manner as Example 1 using thesample A4 as the active material (Comparative example 5).

Comparative Examples 6 and 7

Lithium carbonate (Li₂CO₃) and titanium oxide (TiO₂) having an anatasestructure were mixed. The mixture was sintered at 850° C. for 24 hoursto obtain a spinel type titanium composite oxide (sample A5) of thecomposition formula: Li₄Ti₅O₁₂.

The fact that the resultant substance was a spinel type titaniumcomposite oxide was confirmed by the wide angle X-ray diffraction methodin the same manner as Example 1. The pH of the substance was 11.0.

Next, 100 g of the spinel type titanium composite oxide (sample A5) wasadded to 100 g of water containing 3 g of lithium hydroxide dissolvedtherein. The mixture was left alone in a desiccator at 70° C. whilestirring it to evaporate the moisture. Thereafter, the resultant productwas heated in air at 400° C. for 3 hours to obtain a sample B5. The pHof the sample B5 was 11.2.

The carbon content of the obtained titanium oxide was measured by theinfrared absorption method. As a result, it was confirmed that thecarbon content contained in the sample B5 was 0.62% by mass.

A beaker cell was produced in the same manner as Example 1 using thesample A5 as the active material (Comparative example 6). Further, abeaker cell was produced in the same manner as Example 1 using thesample B5 as the active material (Comparative example 7).

(Measurement of Carbon Content by High Frequency Heating-InfraredAbsorption Method)

The carbon content in titanium oxides and titanium composite oxidesobtained in Examples 1 to 11 and Comparative examples 1 to 6 weremeasured by the high frequency heating-infrared absorption method. Theresults are shown in Table 1 below.

(Infrared Diffuse Reflectance Measurement)

The titanium oxides and the titanium composite oxides obtained inExamples 1 to 11 and Comparative examples 1 to 6 were subjected toinfrared diffuse reflectance measurement with Fourier transform infraredspectrophotometer (FT-IR).

FIGS. 8 and 9 show the results obtained by performing the infrareddiffuse reflectance measurement at 30° C. on each active materialobtained in Example 1 and Comparative example 1. FIG. 8 shows aninfrared diffuse reflectance spectrum at 1300 to 1600 cm⁻¹, and FIG. 9shows an infrared diffuse reflectance spectrum at 2200 to 2500 cm⁻¹.According to the results, in Example 1, absorption peaks around at 1430,1500, and 2350 cm⁻¹, which were considered to be originated fromcarbonate ions (mainly lithium carbonate), were observed. The peaks werenot confirmed in Comparative example 1.

The presence or absence of the peaks at about 1430 cm⁻¹ and 1500 cm⁻¹ inall the examples is shown in Table 1 below.

(Measurement of Battery Performances)

The beaker cells produced in Examples 1 to 11 and Comparative examples 1to 6 were subjected to a constant current charge/discharge cycle ofperforming charging at 1 C and discharging at 1 V (at 25° C. for 3hours) (lithium insertion). Thereafter, a charge/discharge cycle ofperforming charging at 1 C (lithium discharge) up to 3 V was repeated100 times. The ratio of the discharge capacity after 100th cycle to theinitial capacity was calculated as the capacity-maintenance ratio (%).The results are shown in Table 1. The actual capacity of each beakercell is described further in Table 1.

TABLE 1 Negative Carbon Capacity- Actual capacity electrode Peaks at1430, content maintenance after 100 active material pH 1500, and 2350cm⁻¹ (% by mass) ratio (%) cycles (mAh/g) Comparative Sample A1 6.9 Notdetectable (ND) ND 20 or less 52 Example 1 Example 1 Sample B1 8.7Detected 0.12 88 238 Example 2 Sample C1 7.4 Not detectable (ND) 0.01 64172 Example 3 Sample D1 7.6 Not detectable (ND) 0.02 80 216 Example 4Sample E1 7.8 Detected 0.03 86 232 Example 5 Sample F1 9.6 Detected 0.2090 243 Example 6 Sample G1 10.9 Detected 0.41 90 243 Example 7 Sample H112.5 Detected 1.03 88 237 Comparative Sample I1 13.2 Detected 3.02 60(Generation 162 Example 2 of gas) Example 8 Sample J1 8.5 Not detectable(ND) 0.13 86 231 Comparative Sample A2 6.9 Not detectable (ND) ND 20 orless 49 Example 3 Example 9 Sample B2 8.6 Detected 0.12 86 224Comparative Sample A3 7.0 Not detectable (ND) ND 20 or less 43 Example 4Example 10 Sample B3 9.0 Detected 0.13 94 249 Comparative Sample A4 7.1Not detectable (ND) ND 20 or less 38 Example 5 Example 11 Sample B4 9.8Detected 0.19 84 210 Comparative Sample A5 11.0 Detected 0.54 98 161Example 6 Comparative Sample B5 12.2 Detected 0.62 93 153 Example 7

(Infrared Diffuse Reflectance Measurement after Absorption of Pyridine)

Infrared diffuse reflectance measurement after absorption of pyridinewas performed on each active material obtained in Example 1 andComparative example 1. States of the Bronsted (B) acid site and theLewis (L) acid site on the sample surface can be examined by themeasurement. An apparatus and procedures for the measurement are asfollows:

<Diffuse Reflection Measurement Apparatus>

Fourier-transformed type FTIR apparatus: Varian 7000 (manufactured byVarian, Inc.)

Light source: Special ceramic material

Detector: DTGS

Wavenumber resolving power: 4 cm⁻¹

Integration times: 128 or more

Attached device: diffuse reflection measuring device (manufactured byPIKE Technologies Co.)

Reference: gold deposited film

<Measurement Procedure>

[1] A sample powder was directly set in the apparatus to heat up to 150°C. while flowing N₂ at 50 ml/min and then it was maintained at 150° C.for 30 minutes or more.

[2] The temperature of the powder was returned to near the roomtemperature and the powder was heated to 100° C. again.

[3] The pressure of a cell was reduced with an oil diffusion pump,pyridine vapor was introduced into the cell, and the adsorption processwas performed for 15 minutes or more.

[4] The sample powder was heated at 100° C. for 30 minutes or more whileflowing N₂ at 100 ml/min and then it was further heated at 150° C.,followed by maintaining for 30 minutes or more. The physically adsorbedor hydrogen bonded pyridine (HPY) was eliminated, and the in-situinfrared spectrum measurement was performed.

FIG. 10 shows infrared diffuse reflectance measurement results afteradsorption of pyridine in Comparative example 1. In the drawing, thepeak related to the pyridine (BPY) bonded to the Bronsted (B) acid sitewas designated as “B”, the peak related to the pyridine (LPY) boundedthe Lewis (L) acid site was designated as “L”, and the peak related tothe hydrogen bonded pyridine (HPY) was designated as “H”.

In Example 1 and Comparative example 1, values of absorption peak areasaround at 1145, 1538, and 1607 cm⁻¹, originated from the pyridineattached to the acid site of each of the samples (referred to as S1445,S1538, and S1607) are shown in Table 2. As for S1445 and S1538, abaseline was drawn based on each absorption peak originated from thepyridine and the area of the surrounded portion was determined. As forS1607, the peak was split using the Gaussian function (five in the caseof Comparative example 1) and calculated.

TABLE 2 Area of absorption peak of pyridine attached to acid site S1445S1538 S1607 Comparative 4.49 1.65 8.90 Example 1 Example 1 1.15 ND ND

According to Table 2, the B acid site and the L acid site showed highvalues in Comparative example 1. It was found that the solid acid siteconcentration was high. On the other hand, in Example 1, the value ofthe B acid site was lower than the minimum limit of detection. It wasfound that the value of the L acid site was greatly smaller than that ofComparative example 1. Regarding the result of S1445 in Example, thereare contributions of the pyridine bonded to the L acid site (L) and thehydrogen bonded pyridine (H). Since the absorption peak around at S1607cm⁻¹ is hardly observed, the L acid site concentration is considered tobe lower than the minimum limit of detection.

The batteries of Example 1 and Comparative example 1 after the test weredisassembled (lithium release state) and negative electrodes were takenout. The electrodes were sufficiently washed with methylethyl carbonate,followed by IR measurement of the electrode surface. In the IR spectrumof the negative electrode extracted from the battery of Example 1, thepeak of carbonate ion was clearly confirmed at 2350 cm⁻¹. On the otherhand, in the IR spectrum of the negative electrode extracted from thebattery of Comparative example 1, no peak was confirmed.

The extracted negative electrode was subjected to ultrasonic cleaning,only the negative electrode active material was extracted bycentrifugation, the negative electrode active material was heat-treatedat 300° C., and the carbon content in the active material was measuredby the infrared absorption method. As a result, the carbon content ofthe active material extracted from Example 1 was 0.12% by mass, whilethe carbon content of the active material extracted from Comparativeexample 1 was the measurement lower limit or less.

As is clear from Table 1, in the niobium composite oxide represented bythe formula: Li_(x)M_((1-y))Nb_(y)Nb₂O_((7+δ)), the capacity-maintenanceratio (in the charge/discharge cycle test) of the batteries of Examples1 to 11 was higher than that of the batteries of Comparative examples 1and 3 to 5. This showed that the side reaction was suppressed bycontrolling the pH of the niobium composite oxide represented by theformula: Li_(x)M_((1-y))Nb_(y)Nb₂O_((7+δ)). In Comparative example 2,gas generation was significant during the evaluation, and thus stableevaluation could not be performed. This is because the amount of lithiumcarbonate of the sample I1 used in Comparative example 2 was large, andcarbon dioxide gas was generated by a reaction with free acid in anelectrolyte solution. As shown in Table 1, in Comparative examples 6 and7 in which the spinel type titanium composite oxide was used, asufficient actual capacity was not obtained.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

What is claimed is:
 1. An active material for a battery comprising: aniobium composite oxide represented by the formulaLi_(x)M_((1-y))Nb_(y)Nb₂O_((7+δ)), wherein M represents at least onekind selected from the group consisting of Ti and Zr, x, y, and δ arenumbers respectively satisfying the following: 0≦x≦6, 0≦y≦1, and −1≦δ≦1,and the pH of the active material for a battery is from 7.4 to 12.5. 2.The active material for a battery according to claim 1, whereincarbonate ions are arranged on at least one part of the surface of theactive material for a battery.
 3. The active material for a batteryaccording to claim 1, wherein lithium carbonate is arranged on at leastone part of the surface of the active material for a battery.
 4. Theactive material for a battery according to claim 1, wherein the pH is apH measured when the specific surface area of the active material for abattery is from 0.5 to 50 m²/g.
 5. The active material for a batteryaccording to claim 1, wherein the pH is a pH measured when the specificsurface area of the active material for a battery is from 3 to 30 m²/g.6. The active material for a battery according to claim 1, wherein acrystal structure of the niobium composite oxide belongs to a monoclinicsystem.
 7. The active material for a battery according to claim 1,wherein the crystal structure of the niobium composite oxide belongs toa space group C/2m or P12/m1.
 8. The active material for a batteryaccording to claim 1, wherein the carbon content of the active materialfor a battery is from 0.01 to 3% by mass based on the total amount ofthe active material for a battery.
 9. The active material for a batteryaccording to claim 1, wherein the active material for a battery has apeak belonging to the carbonate ion (CO₃ ⁻) in the range of 1430±30, therange of 1500±30, or the range of 2350±30 cm⁻¹ in an infraredreflectance spectrum with Fourier transform infrared spectrophotometer(FT-IR).
 10. A nonaqueous electrolyte battery comprising: a positiveelectrode; a negative electrode comprising the active material for abattery according to claim 1; and a nonaqueous electrolyte.
 11. Abattery pack comprising one or more nonaqueous electrolyte batteriesaccording to claim
 10. 12. The battery pack according to claim 11,wherein the plurality of nonaqueous electrolyte batteries are connectedelectrically to each other, and the battery pack further comprises aprotective circuit that can detect the voltage of each of the nonaqueouselectrolyte batteries.